<?php

require_once("../project/cache_parameters.inc");

if (function_exists("apache_request_headers")) {
    $no_cache = false;
    }
else {
    $no_cache = true;
    }

// mechanism for caching commonly-accessed pages

function make_cache_dirs() {
    if (!@filemtime("../cache")) mkdir("../cache");
    for ($i=0;$i<256;$i++) {
        $j=sprintf("%02x",$i);
        if (!@filemtime("../cache/$j")) {
            mkdir("../cache/$j", 0700);
        } 
    }
}

function get_path($params) {
    if (!@filemtime("../cache/00")) make_cache_dirs();
    $y = pathinfo($_SERVER["PHP_SELF"]);
    $z = $y["basename"];

    // add a layer of subdirectories for reducing file lookup time
    $sz = substr(md5($z."_".urlencode($params)),1,2);
    $path = "../cache/".$sz."/".$z;
    if ($params) {
        $path = $path."_".urlencode($params);
    }
    return $path;
}

function disk_usage($dir) {
    $usage=0;
    if ($handle=@opendir($dir)) {
        while ($file=readdir($handle)) {
            if (($file != ".") && ($file != "..")) {
                if (@is_dir($dir."/".$file)) {
                    $usage+=disk_usage($dir."/".$file);
                } else {
                    $usage+=@filesize($dir."/".$file);
                }
            }
        }
        @closedir($handle);
    }
    return $usage;
}

function clean_cache($max_age, $dir) {
    $start_dir = getcwd();
    if (!chdir($dir)) {
        return;
    }
    if ($handle=@opendir(".")) {
        while ($file=readdir($handle)) {
            if ($file == ".") continue;
            if ($file == "..") continue;

            // don't let hackers trick us into deleting other files!
            if (strstr($file, "..")) {
                continue;
            }
            if (@is_dir($file)) {
                clean_cache($max_age, $file);
            } else {
                if ((time()-@filemtime($file))>$max_age) {
                    //echo "unlinking ".getcwd()."/$file\n";
                    @unlink($file);
                }
            }
        }
       @closedir($handle);
    }
    chdir($start_dir);
} 


// check free disk space every once in a while
function cache_check_diskspace(){
    if (!(rand() % CACHE_SIZE_CHECK_FREQ)) {
       $too_old=86400;
       while ((disk_free_space("../cache") < MIN_FREE_SPACE) ||
           (disk_usage("../cache") > MAX_CACHE_USAGE)) {
           clean_cache($too_old, "../cache");
           $too_old/=2;
       }
    }
}

function cache_need_to_regenerate($path, $max_age){
    $regenerate = false;
        $request = apache_request_headers();

        clearstatcache();
        $lastmodified = @filemtime($path);
        if ($lastmodified) {

            // Check to see if this is a conditional fetch.
            //
            $if_modified_since = isset($request['If-Modified-Since']) ?
                (explode(';',$request['If-Modified-Since'])) :
                false;

            if ($if_modified_since) {
                $if_modified_since=strtotime($if_modified_since[0]);
            }

            if ($if_modified_since && ($if_modified_since == $lastmodified)) {
                Header("Last-Modified: " . gmdate("D, d M Y H:i:s",$lastmodified) . " GMT");
                Header('HTTP/1.0 304 Not Modified');
                exit;
            }

            // See if cached copy is too old.
            // If so regenerate,
            // and touch the cached copy so other processes
            // don't regenerate at the same time
            //
            if ($lastmodified<time()-$max_age) {
                $regenerate = true;
                @touch($path);
            }
        } else {
            $regenerate = true;
        }
    return $regenerate;
}

// Returns cached data or false if nothing was found
function get_cached_data($max_age,$params=""){
    $path = get_path($params);
    cache_check_diskspace();
    if ($max_age) {
	$regenerate=cache_need_to_regenerate($path, $max_age);
	if (!$regenerate){
	    return file_get_contents($path);
	}
    }
    return false; //No data was cached, just return
}

function start_cache($max_age, $params=""){
    global $no_cache;
    if ($no_cache) return;

    $path = get_path($params);
    $lastmodified = @filemtime($path);
    cache_check_diskspace(); //Check free disk space once in a while

    if ($max_age) {
	$regenerate = cache_need_to_regenerate($path, $max_age); //Is the stored version too old, do we need to regenerate it?
        if ($regenerate){
            // If cached version is too old (or non-existent)
            // generate the page and write to cache
            //
            ob_start();
            ob_implicit_flush(0);
            Header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");
            Header("Expires: " . gmdate("D, d M Y H:i:s",time()+$max_age) . " GMT");
            Header("Cache-Control: public, max-age=" . $max_age); 

            // allow the calling page to see cache period
            //
            global $cached_max_age;
            $cached_max_age = $max_age;
        } else {
            // Otherwise serve the cached version and exit
            //
            if (strstr($params, "format=xml")) {
                header('Content-type: text/xml');
            }
            Header("Last-Modified: " . gmdate("D, d M Y H:i:s",$lastmodified) . " GMT");
            Header("Expires: " . gmdate("D, d M Y H:i:s",$lastmodified+$max_age) . " GMT");
            Header("Cache-Control: public, max-age=" . $max_age );
            if (!@readfile($path)) {
                //echo "can't read $path; lastmod $lastmodified\n";
		@unlink($path);
		//Proceed to regenerate content
            } else {
        	exit;	    
	    }
        }
    }
}

// write output buffer both to client and to cache
//
function end_cache($max_age,$params=""){
    global $no_cache;
    if ($no_cache) return;

    // for the benefit of hackers
    if (strstr($params, "..")) {
        return;
    }
    if ($max_age) {
        $path = get_path($params);
        $fhandle=fopen($path, "w");
        $page=ob_get_contents();
        ob_end_flush();
        fwrite($fhandle, $page);
        fclose($fhandle);
    }
}

function set_cache_data($data,$params=""){
    // for the benefit of hackers
    if (strstr($params, "..")) {
        return;
    }
    $path = get_path($params);
    //echo $path;
    $fhandle=fopen($path, "w");
    fwrite($fhandle, $data);
    fclose($fhandle);
}?>
